STRUCTURAL AND COMPOSITIONAL BASIS OF HIGH-TEMPERATURE SUPERCONDUCTIVITY - PROPERTIES OF THE MAGIC ELECTRONIC-STATE

A new electronic model is developed along largely qualitative lines to account for some of the structural and compositional observations in the area of high-temperature superconducting cuprates. The model is based upon the avoided crossing with interatomic separation of two energetically close states, one containing electron holes on copper and the other electron holes on oxygen. If these two curves lie close together, both energetically and configurationally, then a new hybrid state is generated, described at the crossing point by an equal mixture of both. The generation of this slate is very sensitive to copper oxidation level, and small atomic displacements around the energy minimum lead to large changes in the nature of the wave function and, hence, fluctuations in both spin and charge. It is suggested, without proof that this electronic state-of-affairs corresponds to that of the high-temperature superconductor. The variation in the nature of the wave function with distance and, hence, the strength of these fluctuations show striking similarities with the system dependence of the superconducting transition temperature in the cuprate superconductors.